Gain from a better drain

Drainage water management, or controlled drainage, cuts nitrate loads flowing into surface waters through the tile system, especially during the fallow period.

During the growing season, controlled drainage stores moisture and nutrients for the crop, offering the potential for higher yields in dry years.

It was the drought of 1988 that got John Wilken thinking about the wisdom of draining his “liquid assets.”

Wilken, who farms in east-central Illinois, had partly tiled a field before the season started. That dry summer, the undrained portion of his field produced significantly better corn than the drained portion. “That tripped a trigger in my mind, that we should be conserving some of our water for when it’s needed,” he says.

Today, Wilken does just that. He controls how much — and when — tile drainage water leaves 340 acres of flat cropland in Iroquois County.

Using eight outlet control structures in his main tile lines, Wilken can raise and lower the water table depth in two fields. He holds back water in the soil all winter, when drainage isn’t needed for crop production, then releases it about two weeks before field operations begin in the spring.

After planting, he raises the outlet height above the tile depth in order to capture some of the rainfall that would ordinarily drain out. Just before harvest, he drops the outlet back down to the tile depth. In November, after fall strip-tillage and fertilizer application, Wilken raises the outlet height once more, lifting the water table almost to the surface.

This practice — known as drainage water management, or controlled drainage — cuts nitrate loads flowing into surface waters through the tile system, especially during the fallow period, says Don Pitts, a drainage expert for the Natural Resource Conservation Service in Illinois. And during the growing season, controlled drainage stores moisture and nutrients for the crop, offering the potential for higher yields in dry years, he says.

Researchers all around the Midwest are looking for ways to cut pollutants in subsurface drainage water without lowering drainage efficiency. As public concern over water quality intensifies, there is “more interest in what we can do to minimize drainage water volumes and nitrate losses,” says Matt Helmers, an Iowa State University agricultural engineer.

Many new methods are now being tested on Midwest farms, including shallow drainage, constructed wetlands, woodchip biofilters and controlled drainage.

Controlled drainage is widely used on the sandy-soiled eastern and southern coastal plains, often in combination with subsurface irrigation. In Midwest corn and soybean country, though, it’s a new practice that is still being tested.

In 2007, the five-state Agricultural Drainage Management Coalition began side-by-side comparisons of conventional and controlled drainage on 20 farms in Ohio, Indiana, Illinois, Iowa and Minnesota. These demonstrations “will really accelerate our understanding” of the practice, and how it performs across a variety of climates and soils, Helmers says.

In Illinois, where more than 50 on-farm demonstration systems have been installed, drainage water management has cut tile outflow by 40 percent, Pitts says. As tile water volume drops, so does nitrate loss — especially during the winter, when half of annual drainage flow occurs in the eastern Corn Belt.

In the northern Corn Belt, the benefits will probably be more modest, says Gary Sands, a University of Minnesota Extension engineer. There, about 70 percent of annual tile flow occurs from April to June, when growers need drainage most. “So we have a smaller window of opportunity to manage drainage water here,” he says.

Still, northern states could see “20 to 40 percent reductions in the volume of drainage water” and corresponding nitrate loads, Helmers says.

John Wilken grows corn and soybeans on 1,900 acres near Onarga, Ill. In 2002, he installed controlled drainage in a 160-acre field and a 180-acre field. The improvements were cost-shared under the Environmental Quality Incentives Program (EQIP).

Both fields are pattern-tiled with 5-inch laterals every 100 feet to a depth of about 3.5 feet. The ground is very flat, averaging 1 inch of vertical fall per 100 feet, “which makes the system work better,” Wilken says.

The 160-acre field has three outlet-control structures, and the 180-acre field has five. These consist of stacked flashboard risers in the main lines. Wilken adjusts the tile outlet height by manually adding or removing risers.

He raises the outlets in mid-June, “or even earlier if it’s a dry spring,” and leaves them up all summer, “unless we get a 4-inch or 5-inch rain.” By saving moisture in the soil, “I’m confident there’s a 5- to 6-bushel per acre yield increase for corn” in dry years, he says.

Maintaining the water table 2 feet below the surface, rather than the typical 4 feet, retains up to 1.5 inches of additional water in the soil, Pitts says. “This equals about six days’ water supply for a corn crop in July, and thus, could have a significant crop production benefit.”

The cost of controlled drainage depends mainly on the steepness of the field and the size of the tile mains. Retrofitting 81 outlet structures on existing tile systems in Illinois ranged from about $25 per acre on flat sites to more than $250 per acre on sloping fields, Pitts says.

Managed drainage is most economical on land that slopes less than 0.5 percent, or 5 feet of vertical fall per 1,000 feet, says Kevin Ellingson of Ellingson Drainage, based in West Concord, Minn., and Fargo, N.D. Ellingson Drainage has installed half a dozen controlled drainage systems in Minnesota and North Dakota.

“For every 1.5 feet of elevation change, you need an outlet structure to control the water in that zone,” he says.

Dan Jaynes at the National Soil Tilth Laboratory in Ames, Iowa, estimates that about 8.3 million drained acres in Ohio, Indiana, Illinois, Iowa and Minnesota are flat enough to make controlled drainage practical.

On suitable land, a drainage management system amortized over 15 years at 6 percent interest would cost $7 to $9 per acre, according to Leonard Binstock, executive director of the Agricultural Drainage Management Coalition. Yield increases of just 2 or 3 percent could pay for the system.

Controlled drainage is also eligible for EQIP grants, and additional incentives were included in the last farm bill.